When an image recording apparatus such as a color printer performs printing, variations in color may occur on a printed recording material depending on individual model differences, temporal changes, or environmental conditions such as temperature and humidity. For this reason, for example, in an inkjet printer, the amount of ink to be ejected may be changed in accordance with the environmental conditions described above, and variations in color may occur. In an electrophotographic printer, furthermore, the charge ratio of a photosensitive drum may be changed in accordance with the environmental conditions described above, and variations in color may occur. It is known that, in order to correct such variations in color, parameters in output γ correction processing of a color printer or color conversion processing in color matching and color separation are re-generated and updated to perform color calibration.
Methods have been proposed for obtaining a patch chart, which is printed for such color calibration, with high correction accuracy with a limited number of patches. PTL 1 discloses a method for determining gradation values of patches in a patch chart used for calibration. More specifically, a method is described for calculating the total distance of the trajectory of ink droplets on a CIE-L*a*b* space that is a uniform color space (a sum of ΔE over gradations) and determining a gradation of each patch so that distances between patches of adjacent gradations become uniform.